Motion Of System Research Articles

The Star Tug: An active stellar engine capable of accelerating a star to relativistic velocities

Civilizations ahead of our own may wish to control their star system's motion for a variety of reasons, ranging from the avoidance of cataclysmic cosmic events to the facilitation of interstellar, and perhaps intergalactic, colonization. Such an endeavor can be achieved via the construction of megastructures known as stellar engines, which utilize a star's own resources to gradually accelerate the star system in the desired direction over extended periods of time. Here, we conceptualize the ‘Star Tug’, a stellar engine capable of producing significantly higher accelerations than previous stellar engine concepts. The Star Tug consists of an engine positioned ahead of the star along the desired direction of acceleration. The engine is gravitationally bound to the star and utilizes mass acquired from the star as propellant to generate thrust which counterbalances the force of gravity between it and the star. As long as the propellant exhaust velocity exceeds the escape velocity of the star system, the star system should accelerate. Depending on efficiency and engineering constraints, the Star Tug may be capable of accelerating a sun-like star to relativistic velocities within megayear time scales.

Hydrodynamic Instability of Vertical Motions Excited by Spatially Periodic Distributions of Heat Sources

The hydrodynamic instability of a system of vertical motions initiated by spatially periodic distributions of heat sources is investigated. The Galerkin method with three basis trigonometric functions is used to describe the perturbation dynamics. The nonlinear system of equations for finding the expansion coefficients is formulated. It is found that the vertical motions are unstable in the absence of dissipation if the Richardson number is less than one eighth. A weakly nonlinear model of inviscid instability is developed. It is shown that the loss of stability in the presence of dissipation can lead to formation of either steady-state or time-oscillating secondary flow with nontrivial streamline topology.

Effects of blade’s interconnection on the modal characteristics of a shaft-disk-blade system

Present work has further developed a packet blade-disk-shaft coupling model based on previous work to interpret the effects of tuned/mistuned lacing wire on the coupled modal properties. In the developed model, the flexible bladed disk system's swing motion inducing by shaft bending is further considered. Corresponding model validation indicates that the improved model is more accurate than our previous model. Present analysis has three parts: in the first part numerical results focus on the effects of varying lacing wire location (XL) and stiffness ratio (KL) on the coupling behavior between subcomponents. As the lacing wire participating in the coupling vibration, the SDB, DB2, and BB mode shift to LSDB, LDB2, and LB mode, while the TDB mode keeps in constant. The frequency values of new coupling modes conspicuously increase, altering the order of occurrence of the dominant modes as well as the patterns of coupling modes. In the second part, a mistuning severity factor has been introduced to represent the lacing wire damage level and its effects on different coupled modes are summarized clearly. Then further analysis points out that the sensitivity of mode frequencies to lacing wire damage depends on a series of factors. The conclusions can provide a reference for the mistuning identification in the shaft-disk-blade packet system. Finally, the effects of rotational speed on the tuned/mistuned shaft-disk-blade packet are compared and depicted in the Campbell diagram.

Point-to-line last passage percolation and the invariant measure of a system of reflecting Brownian motions

This paper proves an equality in law between the invariant measure of a reflected system of Brownian motions and a vector of point-to-line last passage percolation times in a discrete random environment. A consequence describes the distribution of the all-time supremum of Dyson Brownian motion with drift. A finite temperature version relates the point-to-line partition functions of two directed polymers, with an inverse-gamma and a Brownian environment, and generalises Dufresne’s identity. Our proof introduces an interacting system of Brownian motions with an invariant measure given by a field of point-to-line log partition functions for the log-gamma polymer.

Titanite petrochronology linked to phase equilibrium modelling constrains tectono-thermal events in the Akia Terrane, West Greenland

The Mesoarchean Akia Terrane in West Greenland contains a detailed magmatic and metamorphic mineral growth record from 3.2 Ga to at least c. 2.5 Ga. This time span makes this region an important case study in the quest to track secular changes in geodynamic style which may ultimately inform on the development of plate tectonics as a globally linked system of lateral rigid plate motions. The common accessory mineral titanite has recently become recognised as a powerful high temperature geochronometer whose chemistry may chart the thermal conditions of its growth. Furthermore, titanite offers the potential to record the time-temperature history of mafic lithologies, which may lack zircon. Although titanite suffers from higher levels of common Pb than many other UPb chronometers, we show how measurement of 207Pb/206Pb in texturally coeval biotite may assist in the characterization of the appropriate common Pb composition in titanite. Titanite extracted from two samples of mafic gneisses from the Akia Terrane both yield UPb ages of c. 2.54 Ga. Although coeval, their chemistry implies growth under two distinctly different processes. In one case, the titanite has elevated total REE, high Th/U and grew from an in-situ partial melt, consistent with an identical date to granite dyke zircon. In contrast, the second titanite sample contains greater common Pb, lower total REE, lower Th/U, and grew from dominantly hydrothermal fluids. Zr-in-titanite thermometry for partial melt-derived titanite, with activities constrained by phase equilibrium modelling, indicates maxima of c. 690 °C. Elsewhere in the Akia Terrane, coeval metamorphism linked to growth of hydrothermal titanite is estimated at temperatures of c. 670 °C. These new results when coupled with existing findings indicate punctuated, repeated metamorphic events in the Akia Terrane, in which high temperature conditions (re)occurred at least three times between 3.0 and 2.5 Ga, but crucially changed in style across a c. 3.0 Ga change point. We interpret this change in metamorphism as reflecting a fundamental shift in geodynamic style in West Greenland at 3.0 Ga, consistent with other estimates for the onset of widespread plate tectonic-type processes.

Calculation and exploitation of active anti-roll system

Today, more and more control systems of motion, are applied to different ships. Between the movement of the ship, the movement by rotation causes serious damage to the ship's equipment and their performance. There have been many efforts to invent or create certain equipment in order to eliminate these adverse effects. However, few types of equipment have had the same impact on the stabilization of the rollers and systems with active wings stabilizers. In the recent years have been carried out more research for the improvement of systems of the stabilizer fins. The anti-roll fins are a stabilization, reducing the rolling in the hull of the vessel using the elevator fin general designed on both borders of the keel.

An approach for determining the influence of manufacturing process parameters on product quality characteristics

Abstract Scattering manufacturing process parameters affect the quality of manufactured products, because the product properties deviate from the nominal design. If the desired quality requirements are not met, individual part tolerances can be adjusted in such a way that the required reject rates are achieved. In this context, different methods can be used to determine the individual contributors and to quantify the influence of the individual part tolerances on the quality of the manufactured product. In all existing approaches, however, only geometric tolerances are considered but not the varying manufacturing process parameters that are responsible for the geometrical part deviations. To overcome this, in this article, a novel approach is presented that allows determining the influence of manufacturing process parameters on quality characteristics for systems in motion. The novel approach is also highlighted in a case study of an X-ray shutter.

Rescaling limits of the spatial Lambda-Fleming-Viot process with selection

We consider the spatial Lambda-Fleming-Viot process model for frequencies of genetic types in a population living in R^d, with two types of individuals (0 and 1) and natural selection favouring individuals of type 1. We first prove that the model is well-defined and provide a measure-valued dual process encoding the locations of the `potential ancestors' of a sample taken from such a population. We then consider two cases, one in which the dynamics of the process are driven by events of bounded radii and one incorporating large-scale events whose radii have a polynomial tail distribution. In both cases, we consider a sequence of spatial Lambda-Fleming-Viot processes indexed by n, and we assume that the fraction of individuals replaced during a reproduction event and the relative frequency of events during which natural selection acts tend to 0 as n tends to infinity. We choose the decay of these parameters in such a way that when reproduction is only local, the measure-valued process describing the local frequencies of the less favoured type converges in distribution to a (measure-valued) solution to the stochastic Fisher-KPP equation in one dimension, and to a (measure-valued) solution to the deterministic Fisher-KPP equation in more than one dimension. When large-scale extinction-recolonisation events occur, the sequence of processes converges instead to the solution to the analogous equation in which the Laplacian is replaced by a fractional Laplacian. We also consider the process of `potential ancestors' of a sample of individuals taken from these populations, which we see as a system of branching and coalescing symmetric jump processes. We show their convergence in distribution towards a system of Brownian or stable motions which branch at some finite rate. In one dimension, in the limit, pairs of particles also coalesce at a rate proportional to their collision local time.

Dynamics of finite‐dimensional mechanical systems on Galilean manifolds

AbstractAs presented in the related PAMM contribution ‘Kinematics of finite‐dimensional mechanical systems on Galilean manifolds’, the state space of a time‐dependent finite‐dimensional mechanical system is defined as an affine subbundle of the tangent bundle to the Galilean manifold modeling the generalized space‐time of the system. The second‐order vector field on the state space that describes the system's motion can be associated with a differential two‐form called the action form of the mechanical system. In this paper, we postulate the action form for time‐dependent finite‐dimensional mechanical systems. Moreover, we show that Lagrange's equations of the second kind can be derived as a chart representation of the conditions that define the second‐order vector field which describes the motion.

Edge-Preserving Camera Trajectories for Improved Optical Character Recognition on Static Scenes With Text

Camera systems in fast motion suffer from the effects of motion blur, which degrades image quality and can have a large impact on the performance of visual tasks. The degradation in image quality can be mitigated through the use of image reconstruction. Blur effects and the resulting reconstruction performance are highly dependent on the point-spread function resulting from camera motion. This letter focuses on the motion planning problem for a camera system with boundary conditions on time and position, with the objective of improving the performance of optical character recognition. Tuned edge-preserving trajectories are shown to result in higher recognition accuracy when compared to inverse error and linear trajectories. Simulation and experimental results provide quantitative measures to verify edge-preservation and greater recognition performance.

Residual Setup Errors in Cranial Stereotactic Radiosurgery without 6DoF Robotic Couch

This IRB-approved study was to evaluate the residual interfractional setup errors and intrafractional motion of patients treated with cranial stereotactic radiosurgery without 6 degree of freedom (DoF) couch. We compared a frameless non-invasive vacuum-suction immobilization to a rigid immobilization. Twenty consecutive patients treated by medical linear accelerator or tomotherapy were selected for data collection. The dose and number of fractions received by each patient ranged from 18Gy in 1 fraction (SRS) to 25Gy in 5 fractions (SRT). 12 patients were immobilized using PinPoint, a frameless suction system (Aktina Medical, New York) and 8 patients were immobilized using the Talon rigid screw system. Customized head cushions were used in all patients. 6 out of 12 Atkina patients received pre and post treatment cone beam CT (CBCT) to evaluate the intrafractional motion of the Aktina system. The intrafractional motion with the Talon rigid screw system was previously reported to be negligible thus not repeated in this study. All patients received pre treatment CBCT or megavoltage CT (MVCT) to assess interfractional setup accuracy. Shifts to the final treatment position were determined based on matching bony anatomy in the pre-treatment setup CT and the planning CT. Residual rotational and translational errors were analyzed retrospectively using image registration software. For frameless Aktina system, mean and standard deviation of the intrafractional motions were -0.5±0.7mm (lateral), 0.1±0.9mm (vertical), -0.5±0.6mm (longitudinal), -0.04±0.18°(pitch), -0.1±0.23°(yaw), and -0.03±0.17°(roll) indicating negligible intrafractional motion. Interfractional rotation errors were 0.20±0.69° (pitch), 0.34±0.56° (yaw), 0.35±0.82° (roll) for frameless vacuum-suction immobilization versus -0.10±0.25° (pitch), -0.08±0.16° (yaw), -0.20±0.41° (roll) for Talon rigid screw immobilization showing rigid immobilization setup was more reproducible than frameless immobilization. Without rotational correction by 6DoF couch, residual setup error exists and increases from the image registration center. In a 3D vector space, a tumor located 5cm from the center of image fusion would require a 0.9 mm margin with the Talon system and a 2.1 mm margin with Aktina. With image-guided radiotherapy, translational setup errors can be corrected by image registration between pre-treatment setup CT and planning CT. However, without 6 DoF couch, rotational errors cannot be eliminated. Our study showed that the frameless Aktina immobilization system had negligible intrafractional motion. The interfractional rotation setup error using Aktina was larger than rigid immobilization with the Talon system. For a single lesion away from the center of image registration or for multiple lesions far apart, additional margin may be needed to account for the un-correctable rotational setup errors without 6 DoF couch.

¿Cómo y por qué estudiar la relatividad de la simultaneidad en la escuela secundaria?

Analizamos los resultados obtenidos al poner a prueba dos situaciones que enseñan la relatividad de la simultaneidad en la escuela secundaria. Las situaciones proponen el uso de la suma clásica de velocidades y su no uso, para tomar conciencia de las implicaciones de aplicar conjuntamente el primer y segundo postulado relativista. Se analizan sucesos que ocurren en sistemas de referencia inerciales en movimiento relativo, donde la simultaneidad se pierde según el observador que está en el andén, y no según el que viaja en el tren, a diferencia del conocido problema propuesto por Einstein reproducido mayoritariamente en los textos. Se analizan los protocolos obtenidos en cuatro cursos de grado 11 (15-16 años) con 128 estudiantes de un colegio público de la ciudad de Medellín. Se identifican los invariantes operatorios que utilizan en ambas situaciones, así como las argumentaciones que ofrecen. Los resultados indican que las situaciones propuestas producirían la emergencia y la toma de conciencia de invariantes operatorios vinculados a la relatividad de Galileo, los cuales permitirían conceptualizar la relatividad de la simultaneidad en la escuela secundaria.

Thoracic vertebra fixation with a novel screw-plate system based on computed tomography imaging and finite element method

Background and objectiveThe traditional pedicle screw-rod internal fixation system has been widely used for thoracic diseases in clinical practice, but its high profile increases the damage to soft tissue, leading to long-term intractable back stiffness. The purpose of this study is to compare biomechanical advantages between the new spine pedicle screw-plate internal fixation system and traditional pedicle screw-rod internal fixation system using finite element analysis. MethodsBased on computed tomography (CT), four three-dimensional finite element models of T7-T9 were constructed. The downward concentrated force of 150 N and the moment of 5 Nm was applied to the models to simulate six physiological activities, including flexion, extension, left and right lateral bending, left and right axial torsion. The maximum displacement, range of motion (ROM) and maximum stress of the two models in six physiological activities, was measured to evaluate the biomechanical advantages of the novel pedicle screw-plate internal fixation system. ResultsThe novel pedicle screw-plate internal fixation system has a lower profile than the traditional pedicle screw-rod internal fixation system. With regards to the stability, the maximum displacement of the models of two internal fixation systems decreased by 56.2%–91.4% under the six motion status when comparing with the unstable model. Meanwhile, the ROM remained unchanged between the two models of internal fixation systems besides the left lateral bending. However, there is no significant difference in the ROM between the models of the two internal fixation systems in left lateral bending motion (P = 0.203). In terms of the strength, the maximum stress in the model with the new pedicle screw-plate internal fixation system was higher than that of model with the traditional pedicle screw-rod internal fixation system in every motion status but left and right lateral bending motion. ConclusionsThe novel pedicle screw-plate internal fixation system has lower profile in orthopedics and higher strength, However, it has no disadvantage when comparing with the traditional pedicle screw-rod internal fixation system in terms of the stability. In summary, we suggest that the novel spine pedicle screw-plate system can be used as a new internal fixation and provide better comfort for patients.

Halo approach to evaluate the stress distribution in 3D discrete element method simulation: validation and application to flax/bio based epoxy composite

Discrete element method (DEM) is an interesting alternative to classical approaches as the finite element method (FEM) to simulate homogeneous and heterogeneous materials. Indeed, although DEM was initially developed to simulate granular systems in motion, it also enables to model a continuous medium with the help of a dense granular packing in which the cohesion is introduced between each pair of particles in contact using beam or spring elements. However, among other issues, the local stress field obtained using DEM is heterogeneous, even in the case where it is theoretically homogeneous. In the present contribution, we investigate the stress field distribution in 3D DEM mechanical simulation, and propose an approach we named Halo, to evaluate the level of stress distribution. The idea of the method is to evaluate the stress at the scale of every discrete element (DE) taking into account the contribution of its neighbors, inside the Halo of the DE. The effect of the number of DEs per Halo on the stress distribution is discussed in homogeneous and heterogeneous media. The approach results for homogeneous media are compared to FEM calculations and to the theoretical Hertz solution via a Brazilian test. For the homogeneous media, we use the unidirectional flax/bio based epoxy composite, for which macroscopic longitudinal Young’s modulus is experimentally quantified. Furthermore, comparisons with FEM are performed in this context. Results highlight a good agreement between both approaches in terms of stress fields including extremal values.

Some Features of a Small Spacecraft Application as a Technique for the World Ocean Exploration

Nowadays, space technique is increasingly being used to solve various problems that are not directly related to outer space. One of such problem is the World Ocean exploration by means of Earth’s remote sensing. Middle-class spacecrafts for Earth’s remote sensing are well known, e. g. Resource-P, Spot 8, etc. They have complete attitude control systems and control systems of orbital motion. Using these spacecrafts, it is possible to obtain high-quality information about sea currents, sea animal migrations, environmental conditions, etc. However, such projects are expensive and require a long period of implementation. For this reason, small spacecrafts are widely used now. In contrast with the middle-class spacecrafts, they have a variety of features. The small spacecraft mass does not allow to place a complete attitude control systems and control systems of orbital motion on its board. On the other hand, the small spacecraft moving is little-known. The main perturbing factors for the medium-class spacecraft are aerodynamic and gravitational. The main perturbing factor for the small spacecraft is the magnetic moment. Small spacecraft orbital moving significantly affects on the quality of transmitted to Earth telemetric data. It also affects on the reliability of data about the World Ocean obtained from the small spacecraft. Therefore, the analysis of the small spacecraft rotational motion for Earth’s remote sensing is an important and urgent task. Its solution will allow to obtain qualitative data and to use the small spacecraft for the World Ocean exploration.

Adaptive neural network based position tracking control for Dual-master/Single-slave teleoperation system under communication constant time delays

The novel trajectory tracking control strategies for trilateral teleoperation systems with Dual-master/Single-slave robot manipulators under communication constant time delays are proposed in this article. By incorporating this design technique into the neural network (NN) based adaptive control framework, two controllers are designed for the trilateral teleoperation systems in free motion. First, with acceleration measurements, an adaptive controller under the synchronization variables containing the position and velocity error is constructed to guarantee the position and velocity tracking errors between the trilateral teleoperation systems asymptotically converge to zero. Second, without acceleration measurements, an adaptive controller under the new synchronization variables is presented such that the trilateral teleoperation systems can obtain the same trajectory tracking performance as the first controller. Third, in term of establishing suitable Lyapunov–Krasovskii functionals, the asymptotic tracking performances of the trilateral teleoperation systems can be derived independent of the communication constant time delays. Moreover, these two controllers are obtained without the knowledge of upper bounds of the NN approximation errors, respectively. Finally, simulation results are presented to demonstrate the validity of the proposed methods.

Cosmology with extragalactic proper motions: harmonic formalism, estimators, and forecasts

We conduct a thorough study into the feasibility of measuring large-scale correlated proper motions of galaxies with astrometric surveys. We introduce a harmonic formalism for analysing proper motions and their correlation functions on the sphere based on spin-weighted spherical harmonics, and study the statistics of the transverse velocity field induced by large-scale structure. We use a likelihood formalism to derive optimal estimators for the secular parallax due to the Solar System's motion relative to distant objects, and compute the variance and bias due to peculiar velocities and relativistic aberration. We use a simulated catalogue of galaxy proper motions with radial distributions and noise properties similar to those expected from Gaia to forecast the detectability of the proper motion dipole, whose amplitude may be considered a proxy for the Hubble constant. We find cosmic variance to be the limiting source of noise for this measurement, forecasting a detectability of $1$-$2\sigma$ on a single component of the local velocity, increasing to $2$-$4\sigma$ (equivalent to a 25%-50% measurement of the Hubble constant) if the CMB dipole is included as prior information. We conduct a thorough study into the radial dependence of the signal-to-noise, finding that most of the information comes from galaxies closer than a few hundred Mpc. We forecast that the amplitude of peculiar transverse velocities can potentially be measured with 10$\sigma$ significance; such a measurement would offer a unique probe of cosmic flows and a valuable test of the cosmological model.

Non local branching Brownian motions with annihilation and free boundary problems

We study a system of branching Brownian motions on $\mathbb{R} $ with annihilation: at each branching time a new particle is created and the leftmost one is deleted. The case of strictly local creations (the new particle is put exactly at the same position of the branching particle) was studied in [10]. In [11] instead the position $y$ of the new particle has a distribution $p(x,y)dy$, $x$ the position of the branching particle, however particles in between branching times do not move. In this paper we consider Brownian motions as in [10] and non local branching as in [11] and prove convergence in the continuum limit (when the number $N$ of particles diverges) to a limit density which satisfies a free boundary problem when this has classical solutions. We use in the convergence a stronger topology than in [10] and [11] and have explicit bounds on the rate of convergence.

A computational quantum-mechanical model of a molecular magnetic trap.

A model for describing the states of a molecular system trapped in a cavity created by a fast-rotating strong magnetic field is proposed and implemented. All-particle explicitly correlated Gaussian functions with shifted centers are employed in the model to expand the wave functions of the system. Both "internal" states associated with the system's rovibrational and electronic motions and the "external" states associated with translational motion of the center of mass of the system in the cavity are calculated. The states are visualized by density plots. The model is applied to a trapped HD molecule.

Eccentricity is Not Responsible for Odd Harmonics in HAT-P-7 and Kepler-13A

The exquisite photometry of Kepler has revealed reflected light from exoplanets, tidal distortion of host stars and Doppler beaming of a star's light due to its motion (Borucki 2016; Demory et al. 2012; Welsh et al. 2010; Bloemen et al. 2012). Esteves et al. (2013, 2015) and Shporer et al. (2014) reported additional odd harmonics in the light curves of two hot Jupiters: HAT-P-7b and Kepler-13Ab. They measured non-zero power at three times the orbital frequency that persisted while the planet was eclipsed and hence must originate in the star (Esteves et al. 2015). Penoyre & Sandford (2018) showed that orbital eccentricity could result in time-dependent tidal deformation of the star that manifests itself at three times the orbital frequency and suggested this could be the origin of the measured odd modes. In this Research Note, we show that the small orbital eccentricities of HAT-P-7b and Kepler-13Ab cannot generate the odd harmonics observed in these systems. Esteves et al. (2015) hypothesized that the odd modes could be due to tidal distortion of the star if its spin is misaligned with the system's orbital motion, as is the case in both of these systems (Benomar et al. 2014; Herman et al. 2018), but this mechanism has yet to be verified theoretically or numerically.